* also make factories more consistent by only offering
FlowGraph.create()
* also remove secondary (edge-based) FlowGraph.Builder DSL
* also improve naming for conversions from Graph to
Source/Flow/BidiFlow/Sink
- ActorProcessor terminated eagerly when ConcatAll had just taken up a
new input stream but not yet received onSubscribe for it
- The ActorProcessor eagerly shuts itself down upon onError and that
cannot be changed without completely reworking the Pump, so I opted
for just tracking the outstanding substreamSubscribers that have not
yet seen OnSubscribe and making them cancel properly when that arrives
(possibly later).
* found one bug of too early actor stop and thereby missing cancel of upstream,
in fan-in tests ""work with one immediately failed and one nonempty publisher"
* descriptive name can still be defined with OperationAttributes.name
* revisit all factory methods (apply/create) and implement and document
them in a consistent manner
- Switches from using size-of-1/2 Vectors to using Lists
- Fixes an issue where processorForNode wouldn't use the dispatcher form the settings
- Adds a dedicated Collect fusion op
- Adds various simplifications to ActorBasedFlowMaterializer
- Adds FIXMEs where appropriate
- Switches `grouped` to use a VectorBuilder
- Adds support for `scan`
- ActorBasedFlowMaterializer now uses Iterator instead of head+tail decomp on Seqs
- Identity and Completed Transformers are now cached
- Adds dedicated AstNodes for all combinators
- Adds a hook-in point for fusion in `ActorBasedFlowMaterializer`
- Adds support for `Operate` an AstNode with a function that create a fusing.Op
- Adds experimental and slow optimizer as a PoC
- Adds verification that Ast.Fused does not exist in optimizer input
